According as a magnetic recording medium is miniaturized and its recording capacity is increased, the relative velocity between a readout magnetic head and the magnetic recording medium (magnetic disk) has been reduced. Thus, a magnetoresistive head (hereinafter referred to as `MR head`) has attracted attention since its reproduction power does not depend on velocity. Such a MR head is discussed in R. P. Hunt et al., "A Magnetoresistive Readout Transducer", IEEE Trans. on Magn., Vol.MAG-7, No.1, pp.150-154(1971).
Known as a most practical MR head device is a magnetoresistive merged head (or merged head device) with both a MR head and an inductive head.
In such a merged head device, the MR head with a reproducing function is, as shown in FIGS. 1 and 2, composed of two strip-shaped magnetic shield films 53, 54 which are parallel disposed on a common plane and are opposite to a magnetic recording medium (magnetic disk, not shown), and a magnetoresistive effect element (not shown) which is located through a magnetic separation layer of an insulator between the two magnetic shield films 53, 54.
Also, the inductive head(hereinafter referred to as `ID head`) is, as shown in FIGS. 1 and 2, composed of one magnetic pole film which corresponds to the other magnetic shield film 54 of the two magnetic shield films 53, 54, and a coil(not shown) to be sandwiched by an insulator and the other magnetic pole film 55 which are formed parallel with one magnetic pole film 54 on a plane on the other side of the magnetic pole film 54 (other magnetic shield film) where the magnetoresistive effect element does not exist. Thus, the recording is conducted by magnetic field which generates at a magnetic gap G.sub.ID to be given between the magnetic pole films 54, 55. Herein, 51 is a slider main body and 52 is aluminum film for protecting the device. Also, 55A, 55B are concave portions disposed on both sides of the other magnetic pole film 55.
In merged head devices where a MR head and an ID head are layered, there is a problem that the positions of these two heads and the gap may be relatively varied due to a failure in alignment on photolithography in fabrication process.
Further, in merged head devices, there occurs rather a big side-fringing magnetic field during recording. This magnetic field is formed by the leakage of magnetic flux to one magnetic pole film 54 caused by that the width of the other magnetic-pole film 55 is greater than that of one magnetic pole film 54.
Also, due to the side-fringing magnetic field, a minimum track width to be achieved is limited and an upper limit of track density is thereby limited. Thus, to achieve a high-density recording by using a merged head device, the minimizing of side-fringing magnetic field is necessary.
In conventional ID head devices for recording and reproducing, the side-fringing magnetic field is reduced to be minimum since respective planes to define a track width on a plane opposite to a recording medium(air bearing surface plane, hereinafter referred to as `ABS plane`) of magnetic pole films 54, 55 are formed to substantially coincide with each other, i.e., to give a common plane.
However, in the merged head devices, one magnetic pole film 54 has to have a width much greater than that of the other magnetic pole film 55 to define a track width so as to shield the MR element. Therefore, such a wide phase causes the side-fringing magnetic flux extending laterally beyond the width of the other magnetic pole film 55.
Japanese patent application laid-open No. 7-262519 (1995) discloses a method for reducing the side-fringing magnetic field like the conventional ID head devices. In this method, as shown in FIG. 3, there is provided a protruded magnetic pole 54a which has a plane orthogonal to the surface of one magnetic pole 54 as well as being parallel with the surface of one magnetic pole 54 and having the same width as the other magnetic pole 55 and are magnetically connected to one magnetic pole(other magnetic shield) 54, between one magnetic pole (=other magnetic shield) 54 of a recording ID head and magnetic gap G.sub.ID. Thus, a recording magnetic field is generated between the protruded magnetic pole 54a and the other magnetic pole 55. Therefore, the side-fringing magnetic flux can be suppressed like the conventional ID head devices.
In FIG. 3, 64 is a MR head, 65 and 66 are end regions of the MR head 64. Also, 64A and 64B are an upper gap and an lower gap, respectively of the MR head 64.
A method of making the protruded magnetic pole 54a will be explained in FIGS. 4A to 4D.
First, the magnetic gap G is formed on one magnetic pole 54 (P1) also used as the other magnetic shield of the MR head 64, and then a magnetic shield P2 with a predetermined width is formed by frame plating to be defined by photoresist frames 74, 75. Then, by using this magnetic shield P2 as a mask, one magnetic pole 54 is etched by a desired depth by ion beam milling, thereby forming the protruded magnetic pole P3 (54a). In this case, by setting optimally an angle of ion beam B, the magnetic pole P2 and protruded magnetic pole P3 (54a) can be formed to be orthogonal to one magnetic pole 54 (P1).
Also, by providing the protruded magnetic pole P3 (54a) with a desired height, the recording magnetic flux can be substantially defined between the protruded magnetic pole P3 (54a) and the other magnetic pole P2 (55), thereby reducing the side-fringing like the conventional ID head devices.
Thus, in the above method of making the merged head device, the ion beam milling is used to form the protruded magnetic pole P3 (54a). As the milling proceeds, the film thickness of the other magnetic pole P2 (55) decreases since the magnetic pole P2 (55) functions as a mask. Namely, to obtain a desired film thickness of the other magnetic pole P2 (55) when the protruded magnetic pole P3 (54a) is formed, it is necessary that a decrease in the film thickness of the other magnetic pole P2 (55) due to the ion beam milling is previously estimated.
Also, in the this method, the photoresist frames 74, 75 need to have a height much greater than a conventional one so as to form the initial magnetic pole(other magnetic pole) P2 (55) by frame plating. Namely, the film thickness of the other magnetic pole P2 (55) after milling is reduced. Therefore, the other magnetic pole P2 (55) before milling needs to have a much greater film thickness.
On the other hand, when the height of the frames 74, 75 is increased to get a sufficient film thickness, it generally becomes difficult to narrow the frame interval. In Japanese patent application laid-open No. 7-262519, the limit of the frame interval is reported to be 2 .mu.m. In other words, the method disclosed in Japanese patent application laid-open No. 7-262519 is difficult to give a merged head device for high-density recording with a track width less than 2 .mu.m.
As described above, in the merged head device composed of MR head and ID head, there is a problem that the head with a narrower track width is difficult to fabricate, while it solves a failure in alignment of MR head and ID head and side-fringing of recording magnetic field in ID head.
To solve this problem, there is proposed a method that the width control of the magnetic pole 55(P2) and formation of the magnetic pole 54a(P3) are conducted by ion beam etching from the ABS plane, without controlling the width of the magnetic pole 55(P2) of ID head and forming the magnetic pole 54a(P3) with the same side surface as the magnetic pole 55(P2) on the magnetic pole 54(P1) by wafer treatment.
In this regard, M.Yoshida et al.,"Edge Eliminated Head", IEEE Trans. on Magn., Vol. 29, No. 6, pp. 3837-3839 (1993) reports a method that ion beam etching from ABS plane is conducted to suppress undershoots in the readback signal of inductive thin film heads.
However, when this method is applied to a head for high-density recording, such as a merged head of MR head and ID head, dust may be frequently caught in a concave portion formed by ion beam etching since the clearance between head and medium is very short. In the worst case, it may cause a head crash.